This chapter begins with an introduction on the topic, that is, sunflecks and their importance to forest understorey plants. Sunflecks occur when predominantly direct-beam radiation passes through openings in the forest canopy. Measurement of sunfleck activity beneath forest canopies through various techniques namely, area-survey techniques, instaneous sensor measurements, photographic techniques, is discussed. Sunfleck activity in temperate and tropical forests is discussed. Photosynthetic responses to sunflecks has also been explored in the chapter, wherein, sunflecks and carbon gain to understorey habitats, determinants of sunfleck utilization, constraints on sunfleck utilization in understorey habitats, sunfleck regimes and light acclimation, and photosynthesis in understorey plants have been discussed. The chapter reviews seed germination and establishment in understorey habitats and growth of understorey plants in relation to sunflecks. The chapter then turns to the discussion of the influence of sunflecks on reproductive behavior and distributions of understorey species wherein it discusses about light availibility, size variations and reproductive behavior; then vegetive and sexual reproductive effort; sunflecks, canopy gaps and species distributions; and vertical distribution of understorey species. Finally the chapter closes with conclusion about the importance of sunflecks: scaling up from leaves to whole plants and directions for future research.